Up to recent times, this result was obtained with the aid of manually manoeuvred adjusting flap valves, constituted in fact by apparatus similar to slide valves. As initial adjustment of the flap valves proved to be delicate and the characteristics of the installation varied in time, automatically operating regulators have been proposed, making it possible, by modifying the section of air passage, to obtain a constant flowrate whatever the variations in the pressure inside the conduits.
In known regulators, the section of passage is modified with the aid of a mobile member on which the pressure of the air conveyed and suitably arranged elastic means act in antagonism. However, experience has shown that the constructions proposed are complex and expensive, frequently prove to function noisily and present a range of regulation of low amplitude, unstable in time.
It is an object of the present invention to overcome these drawbacks.